But what's wild is that this “sexy diet trend” has been around for almost a century, and was originally used to treat epilepsy. In the 1920s, doctors discovered that starvation forces the body to burn acid-forming fat for energy. And acid, aka "ketones," is actually beneficial for people with epilepsy, because it lowers brain electricity, which can prevent seizures from occurring.

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This was a major medical breakthrough, but doctors quickly realized that fasting is not a sustainable long-term solution for anyone (people require food to live, after all). Luckily, they figured out that a low-carb, high-fat diet could lead to the same results, and be just as effective for treating epilepsy. Thus, the "ketogenic diet" was born.

The ketogenic diet involves eliminating carbs so that the body goes into what's called "ketosis," explains Melissa Matteo, MS, RD, LD, CDE, a registered dietitian and certified diabetes educator at Cleveland Clinic. "In the state of ketosis, your body is burning its stored fat as a source of fuel, and it's only going to do this in the absence of carbs," Matteo says. Without carbs, your body essentially has no choice but to turn to fat stores.

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The key with [the keto diet] is it has to be medically monitored, meaning there really should be a doctor overseeing it.

Melissa Matteo, MS, RD, LD, CDE

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But here's the deal: While the ketogenic diet has become a celebrity-endorsed lifestyle trend in the past few years, it's an extremely restrictive diet that is not for everyone. "The key with [the keto diet] is it has to be medically monitored, meaning there really should be a doctor overseeing it," Matteo says.

For example, when Matteo instructs patients to go on the ketogenic diet, they first have to get lab work to see if they have any electrolyte imbalances, and she will closely monitor uric acid levels throughout the diet, because those tend to be elevated during a high-protein low-carb diet and can lead to gout. "There's also supplementation that's required, because it's so restrictive, and you're really eliminating certain food groups," she says. Matteo will work with a doctor to figure out which supplements patients need to take to make up for the vitamin depletion.

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A true ketogenic diet is intense and difficult to adhere to. On the ketogenic diet, 70-80% of your daily calories come from fat, and about 5% come from carbohydrates, which can be a huge change for most people. (The Dietary Guidelines for Americans recommends that carbs make up 45-65% of your total daily calories, for comparison.) So, on keto you're eating around 20 grams of carbs a day, and that includes fruits and vegetables. You're not supposed to eat starchy foods like bread, rice, potatoes, or beans. No dairy, including milk and yogurt, and absolutely no sugar, either. "They're mainly going to be eating protein and fat, and usually very small amounts of non-starchy vegetables like broccoli, green beans, Brussels sprouts," Matteo says.

The only way to truly tell if it's "working" and you're in a state of ketosis is to test your urine for ketones, Matteo says. You can buy something called "keto sticks," which measure the amount of ketones, "almost like testing chlorine levels in a pool," she says. In a clinical setting, the ketogenic diet serves a very important purpose: to help people lose weight for health reasons. "I definitely would not recommend it to people without knowing their eating habits or medical history," she says.

Certain people should not go on the ketogenic diet, because it can lead to further health issues. For example, if you're prone to gout, it's not a good idea to go on a keto diet, because ketones are acidic, Matteo says. Additionally, if you've had any type of cardiac issues or kidney disease, then rapid weight loss could spark complications. "Sometimes people don't even know that unless they were evaluated by a doctor," she says. For these reasons, those who heard about keto through celebrities or word of mouth need to be extra careful, she says.

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To be fair, some people, like those with epilepsy, do really benefit from a ketogenic diet. There's evidence that the keto diet can improve blood sugar levels in people with diabetes. And some studies suggest that the keto diet could be helpful for managing polycystic ovarian syndrome, certain neurological diseases, and even acne. On the other hand, some athletes like Lebron claim that the keto diet helps them perform, yet recent studies have shown that the diet actually inhibits athletic performance. So, there's still a lot about the effects of keto diet that we don't quite know yet. And unless you have a doctor and a registered dietitian to guide you safely through the eating plan, it might not be worth it.

Like so many diets, what works for one person — or a handful of celebrities — may not work for you. "If somebody's interested in this, they just need to do their homework, and really research what it all entails," Matteo says. That means understanding what this will entail in the short term, but also long term. A diet as rigid and limiting as the ketogenic diet comes with a lot of caveats and risks, because ultimately you're drastically changing your diet and eliminating necessary — and very delicious — nutrients.